The present invention relates to a high-voltage power switch of the type having a stationary contact, an axially displaceable contact, a nozzle through which compressed gas flows from a compression chamber to an expansion chamber during quenching of an arc, and an electromagnetic coil surrounding the stationary contact.
A switch of this type is disclosed in European Patent Application No. 4,213. In this type of switch, an electric arc burns initially during disconnection of the stationary contact and the moving contact. As soon as the bases, or end points, of the arc are at a certain distance from each other, the base located on the stationary contact migrates onto an annular contact connected to one terminal of a coil, the other terminal of the coil being electrically coupled with the stationary contact. When the arc has been commutated to the annular contact, the current to be interrupted flows through the coil. The magnetic field of the coil causes the arc to rotate, whereby the surrounding compressed gas is heated and the extinction of the arc is effected.
The rotation of the arc on the annular contact provides a significant advantage in that the formation of metal vapors is largely prevented, assuring high dielectric strength in the distance between the separated contacts. Immediately following the contact separation, prior to the commutation to the annular contact, the arc is burning between the stationary and the moving contacts, without a significant local displacement of its bases. Depending on the magnitude of the current to be disconnected, burned parts and metals are evaporated; reducing the dielectric strength of the arc path.
The main object of the invention is therefore to provide a novel high voltage power switch wherein an increase in the dielectric strength of the arc path is effected by simple means and the commutation of the arc onto the annular contact is accomplished safely.
This object is attained by providing a radial exhaust channel between the stationary and annular contacts to enable the insulating gas to flow into an expansion chamber. The switch according to the invention achieves its objective by causing combustion products and metal vapors, which are produced between the contacts in the course of each switching process and which reduce the dielectric strength of the contact-break path, to be removed from the heated compression chamber, and thus from the arc path, and transported into a closed, cooled discharge chamber, wherein they are deposited on the walls in the form of solids. The dielectric properties of the compressed gas used to extinguish the arc are thereby significantly improved. Furthermore, the communication of the arc from the stationary contact to the annular contact is always achieved with certainty, since an outwardly directed radial flow of compressed gas is present during the entire disconnecting phase.
By providing two expansion chambers connected by a one-way valve, the return of the arc, after commutation, from the annular contact to the stationary contact is safely prevented even during the disconnection of a very large current, because the flow of the quenching gas is always directed in a radially outward direction. Therefore, if in the course of the disconnection of an extremely large current, the quenching gas in the part of the compression chamber defined by the stationary contact and the annular contact is heated to the extent that the volume of the discharge chamber is unable to receive the radially outward flowing gas completely, the gas conducted into a supplemental volume once it reaches a predetermined value of pressure.
It is convenient to design the discharge chamber with porous or sintered walls, since in this manner the heated quenching gases are cooled better and the combustion and metal parts volatilized by the arc are condensed more rapidly.
Further in accordance with features of the invention, an axially movable pin can be used to close off an orifice in the movable contact during part of the disconnecting operation, so that during the switching of small currents, the pressure of the quenching gas is built up in the commutating chamber to a level sufficient to insure the commutation of the arc from the stationary contact to the annular contact. A particularly effective blowing of the arc is obtained when the switch according to the invention is designed with a pin having the shape of a nozzle.
The features and advantages of the present invention will become more apparent from a perusal of the following detailed description of a preferred embodiment thereof illustrated in the accompanying drawings.